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Configuration Memory
Micro
Channel Architecture Handbook, Chester A. Heath, pages
154-155 PS/2 RTC / CMOS Batteries By Bob Eager and Peter Wendt Reworking Dallas RTC Modules by Peter Wendt One facet of Micro Channel is the effort IBM made with the technology available AT THAT TIME to overcome previous limitations. Period computers were limited to a few Megabytes of RAM and 8086 CPUs. Three components of configuration memory Tomas Slavotinek wrote: RTC - RTC registers CMOS - "internal SRAM" which is internal to RTC NVRAM - "Extended CMOS" which is external to RTC The battery always backs up the RTC and its internal SRAM ("CMOS"). But like Dave mentioned, the 25/30 8086 planars use the very primitive NS MM58167 RTC, which only has space for clock-related values. Since there are no user fields in the internal SRAM [CMOS], these systems are auto-configured during POST. As far as I know, all other systems have RTCs with user-defined storage, using this area for system configuration. Earlier systems with more than 4 MCA slots use extended CMOS ("NVRAM") to store additional configuration data. This is necessary because the SRAM of older RTCs is too small to fit POS data for 8 slots along with the planar config and other info. Earlier system's NVRAM is 2KB. Later systems have RTCs with bigger SRAM, but they also store significantly more data, not just configuration-related info but also error logs, VPD, etc. So, the external NVRAM is still needed (either 2 KB or 8 KB). Modern RTC and NVRAM chips can operate at lower voltages (as low as 2.5 V for some Dallas chips) and likely have lower power consumption when in power-down mode. 6V versus 3V Battery MAJ Tom waxes lyrical: The 6 V battery was likely chosen for its higher voltage and larger capacity. The older RTCs, like the MC146818 used in the Model 80, require higher operating voltage - between 3 and 6 V. If you check the Model 80 schematic, you'll see that there are 3 diodes in series on the +Vbat rail (ignoring the additional two PSU/Batt blocking diodes). This drops the voltage supplied to the chip by about 0.6 V * 3 = 1.8 V. So, the choice wasn’t made solely for the higher voltage. It's a compromise - the chip consumes less power at lower Vcc, but you can’t drop the Vcc too much; it needs to stay above 3 V for as long as possible, ideally only dropping below that during the final phase of the battery discharge curve when the voltage starts to sharply decline. This way, you maximize battery life. It's a fine balance... Effect of a Dying Battery Everything is rated for operation over a Min / Max voltage range. So when a battery is dying, you are drifting towards the Min voltage needed to reliably operate the RTC / NVRAM. As with all ICs, each device has tolerances, some take less power, others take more. So you are flogging your PS/2, trying to install and configure adapters -OR- system devices. The battery is trying, but it has one foot in the grave... It's a toss of the dice, whether it has enough oomph to write all of the configuration values correctly. In the case of a truncated POSID, the POS mechanism does not extrapolate the missing bits of the POSID, it just sets an error message and waits for you to fix it. Even better, the low voltage may result in writing to the wrong address. This makes troubleshooting a system with a corrupt RTC / NVRAM difficult. You try to clear it, but little gremlins hold on to the corrupted bits in random locations. Recovering from a dead battery can be SIMMple as pulling the dead battery, moving the Password Clear jumper, and installing a new battery. Other times might require shorting the RTC [discrete implementations] as well. Adding External Battery to RTC Module At first, one might be seduced by the ideal of dremelling away the epoxy body of an RTC module, exposing the Vcc and Vdd pins, then soldering on leads to an external battery. Not a good solution, now the molded-in lithium cell [flat] is in parallel with a new battery. The resulting voltage will be low volts plus full volts, average that, and it is less than what you need. That is why various mods involve exposing the Vss and Vdd leads inside the epoxy, cutting them, then connecting the leads for an external holder to the RTC module. -OR- a more invasive technique is to expose the moulded-in RTC module's lithium cell, removing it, then connecting the leads for an external holder to the RTC module. RTC / CMOS Battery Types 8509237 RTC module [1x Dallas DS1287] 33F8354 3 V coin cell [1x CR2032 coin cell] Soldered 3 V battery [1x BR-⅔A lithium cell] 72X8498 6 V [1x CR-P2 lithium cells in a pack] 64F9987 6 V [2x CR2477 coin cells in a pack] MAJ Tom wrote: SRAM and CMOS logic in general draws minimal power when not switching states (essentially just dealing with leakage current of the transistors). It's the state transitions (switching) what causes the biggest power draw. So it's not just the register updates that consume power but also the other logic that's constantly updating during operation, like clock dividers. This is why the MC146818A RTC draws 100x more power when it's driven by a high-speed 4 MHz or 1 MHz clock source compared to the standard 32.768 kHz crystal. The higher frequency significantly increases the switching activity.. List of RTC Configurations by Model There are a few different configurations that you will see: Oops, sorry, the NVRAM amounts are... wrong. 8560, 8570, 8580, 8573-P73/P75, Motorola MC146818AFN RTC/CMOS 2kx8 SRAM (NVRAM) 32.768 kHz xtal 6v Lithium in battery / speaker holder 8580-Axx 8kx8 SRAM ? 8556/8557, 9556/9557, 9576/9577 DS1210S Nonvolatile Controller Chip Dallas DS1285 Real Time Clock [Direct replacement for MC146818A] 2kx8 SRAM (NVRAM) 32.768 KHz xtal 8590, 8595 DS1210 Nonvolatile Controller Chip Dallas DS1285 Real Time Clock [Direct replacement for MC146818A] 8Kx8 SRAM (NVRAM) 32.768 KHz xtal CR2032 3v coin cell 8555, 8565SX The much cursed DS1287 Dallas DS1287 [all-in-one, quartz, battery and RTC] Dallas DS1220AD 2Kx8 NVRAM [65SX] Period View of Configuration Memory Passage from the holy MCAH [Praise be to Chet Heath! We are NOT worthy!] "The options for storing configuration data are considerable. Any form of storage accessible to the computer could be used. The information could be stored in the form that it was exchanged, on floppy disk. That, however, creates additional problems. For instance, it makes operating the system dependent on having a disk with the right information on it available to the machine at all times. If something happens to the disk, or if, perhaps, the wrong floppy is put in a slot, the machine would literally lose its mind. Solid-state memory is the more viable option. However, the solid-state memory must be changeable without being volatile. For example, all of the set-up information could be put in immutable ROM memory, but such an arrangement would not allow the needed flexibility of altering set-up parameters to avoid conflicts between competing expansion boards. ROM lacks the needed changeability. While standard RAM memory is changeable, it is volatile. As a result, if set-up information were stored in RAM, each time the machine was booted it would have to be set up afresh. EEPROM Technology Two memory technologies meet the criteria for nonvolatility and changeability, EEPROM (electronically erasable programmable read-only memory) and CMOS (complimentary metal oxide semiconductor) RAM backed up with battery power. The EEPROM technique uses special memory chips that normally function as ROM memory but can be programmed while inside an active computer. By sup- plving a special voltage to an EEPROM chip, the contents of its memory can be erased and new information stored inside it. Like normal ROM, the contents of EEPROM do not change, even when power is totally removed from the system and the chips. The disadvantages of EEPROM include short life - typically EEPROM chips are slow and rated for only thousands of erasures and rewritings over their total lifetimes. A few service or diagnostic operations that would exercise EEPROM circuitry (remember, it has to be tested, too) could end the life of a computer in an attempt to lengthen it. The short life of the EEPROM module can thus determine the useful life of an entire computer system. CMOS Memory On the other hand, battery backed-up CMOS chips are faster than EEPROM and work almost eternally (CMOS memory chips can be repeatedly updated millions of times per second without degrading). Moreover, EEPROM requires special support circuitry to handle the erasures and rerecording of data which CMOS does not. Recent advances in EEPROM technology may someday allow its use for POS option retention. CMOS RAM chips are simply standard RAM chips that have been specially designed to consume a minimum amount of power, a tiny fraction of standard memory. This same kind of energy-frugal circuitry is found in most electronic watches - the kind that need only a tiny new battery every few years. Otherwise, CMOS memory can be read and written to exactly like standard RAM. CMOS is also equally as volatile as standard RAM. However, because its power consumption is so miniscule, the contents of CMOS memory can be maintained for long periods, even years, using no more electricity than is available from a typical battery. Backing CMOS with a battery creates a very good system for holding configuration information. It's actually the same system used in earlier AT-style computers for handling the modest set-up parameters of those machines—usually little more than hard-disk types and the amount of memory installed in the system. POS just uses more CMOS memory to store more and more particular set-up information. The one weakness of the CMOS-and-battery technique is that, when the battery dies, so does the information stored in the set-up memory of the computer. Since battery life is measured in years, this problem was regarded as a minor trade-off to obtain an overall better system. Moreover, when the battery dies, the system can either be set up as it was initially or the set-up information can be reloaded from a record of the configuration stored in a floppy or hard disk file. " PS/2 Configuration Memory Method by Model I am not saavy on 8525 and 8530 systems... Also, this list has NOT been verified. 8525-8086 U38 SRM2264M ? [piezo speaker] Type 1, 2, and Japanese 8586-8086 No RTC 8525-286 [piezo speaker] Dallas DS1287 [all-in-one, DS1285, quartz xtal, lithium battery] 8525-SX [piezo speaker] 32.768 kHz xtal 33F8354 3 V coin cell [1x CR2032] 8530-8086 No NVRAM [piezo speaker] MM58167AN 32.768 kHz xtal 3v Lithium battery soldered to riser 8530-286 [piezo speaker] Dallas DS1287 [all-in-one, DS1285, quartz xtal, lithium battery] 8533 SX No data 8535/8540 SX, LS, SLC Dallas DS1287 [all-in-one, DS1285, quartz, lithium battery] 8543 SX 32.768 kHz xtal 8550 [limited to RTC only!] Motorola MC146818A RTC 32.768 kHz xtal 72X8498 6V pack in battery / speaker holder [1x CR-P2 lithium] 8550z [limited to RTC only!] Motorola MC146818A RTC 32.768 kHz xtal 72X8498 6V pack in battery / speaker holder [1x CR-P2 lithium] 8551 N51 No data 8553 Dallas DS1387 RAMified RTC 4K x 8 [embedded Lithium cell] 8554 CL57 SX No data 8555 SX/LS Dallas DS1287 RTC/CMOS [Lithium cell, quartz crystal, write protection circuits] 8556/8557 SX, SLC Dallas DS1210S NVRAM controller Dallas DS1285 Real Time Clock [Direct replacement for MC146818A] 32Kx8 SRAM (NVRAM) 32.768 KHz xtal 8560 Motorola MC146818A RTC/CMOS 32.768 kHz xtal 72X8498 6V pack in battery / speaker holder [1x CR-P2 lithium] 8565SX Dallas DS1287 RTC/CMOS [all-in-one, DS1285, quartz, lithium battery] Dallas DS1220AD 2Kx8 Nonvolatile SRAM [lithium cell] 8570 Type 1 Motorola MC146818A RTC/CMOS 2kx8 SRAM 32.768 kHz xtal 72X8498 6V pack in battery / speaker holder [1x CR-P2 lithium] 8570 Type 2 Motorola MC146818AFN RTC/CMOS 2kx8 SRAM 32.768 kHz xtal 72X8498 6V pack in battery / speaker holder [1x CR-P2 lithium] 8570 Type 3 Motorola MC146818AFN RTC/CMOS 8kx8 SRAM 32.768 kHz xtal 72X8498 6V pack in battery / speaker holder [1x CR-P2 lithium] 8573 P70 Old Motorola MC146818A RTC 32 KHz xtal 72X8498 6V pack in battery / speaker holder [1x CR-P2 lithium] 8573 P70 New MC146818 MC146818AFN RTC 32.768 KHz xtal 72X8498 6V pack in battery / speaker holder [1x CR-P2 lithium] 8573 P75 MC146818AF RTC 32.768kHz xtal 64F9987 6v pack in battery / speaker holder [2x CR2477 coin cells] 8580 Type 1 Motorola MC146818A RTC 2Kx8 SRAM (NVRAM) 32.768 kHz xtal 72X8498 6V pack in battery / speaker holder [1x CR-P2 lithium] 8580 Type 2 Motorola MC146818A RTC 2Kx8 SRAM (NVRAM) 32.768 kHz xtal 72X8498 6V pack in battery / speaker holder [1x CR-P2 lithium] 8580 Type 3 Motorola MC146818AFN RTC/CMOS 2Kx8 SRAM (NVRAM) 32.768 kHz xtal 72X8498 6V pack in battery / speaker holder [1x CR-P2 lithium] 8590 Dallas DS1210 NVRAM controller Dallas DS1285 Real Time Clock [Direct replacement for MC146818A] 8Kx8 SRAM (NVRAM) 32.768 KHz xtal 33F8354 3 V coin cell [1x CR2032] 8595/9595 SS/SP Dallas DS1210 NVRAM controller Dallas DS1285 Real Time Clock [Direct replacement for MC146818A] 8Kx8 SRAM (NVRAM) 32.768 KHz xtal 33F8354 3 V coin cell [1x CR2032] 9533 486SLC2 NVRAM in VLSI VL82C306-FC1 ? 32.768 KHz xtal 33F8354 3 V coin cell [1x CR2032] 9552 700 Dallas DS1485S RTC/CMOS/NVRAM 32.768 kHz xtal 9552 720 Dallas DS1485S RTC/CMOS/NVRAM 32.768 kHz xtal 9556/9557 Dallas DS1210S NVRAM controller Dallas DS1285 Real Time Clock [Direct replacement for MC146818A] 32.768 KHz xtal 33F8354 3 V coin cell [1x CR2032] [battery holder on MCA riser] 9576/9577 Bermuda Dallas DS1210S NVRAM controller 8Kx8 SRAM (NVRAM) 32.768 KHz xtal 33F8354 3 V coin cell [1x CR2032] [battery holder on MCA riser] 9576/9577 Lacuna Dallas DS1585S RTC/CMOS + 8Kx8 NVRAM 32.768 KHz xtal 33F8354 3 V coin cell [1x CR2032] [battery holder on MCA riser] 9585 Type 1 [X] Dallas DS1485S RTC/CMOS/NVRAM 32.768 kHz xtal 33F8354 3 V coin cell [1x CR2032] 9585 Type 2 [K/N] Dallas DS1585S RTC/CMOS + 8Kx8 NVRAM 32.768 kHz xtal 33F8354 3 V coin cell [1x CR2032] 9595A DS/DP Dallas DS1585S RTC/CMOS + 8Kx8 NVRAM 32.768 KHz xtal 33F8354 3 V coin cell [1x CR2032] RTC Varieties DS1210S Nonvolatile Controller Chip "S" 16-Pin SOIC (300 MIL) Converts CMOS RAMs into nonvolatile memories DS1285/DS1285Q Real Time Clock "Q" 28-pin PLCC Direct replacement for MC146818A DS1485/DS1488 RAMified RT Clock 8K x 8 NVRAM Upgraded IBM AT computer clock/calendar with 8K x 8 extended RAM DS1488 stand alone module with DS1485, embedded lithium battery and crystal DS1585/DS1587 Serialized RTC Industry standard DS1287 PC clock plus enhanced features DS1587 incorporates DS1585 chip, 32.768 KHz crystal, and a lithium battery MC146818A Real-Time Clock plus RAM |